1. Field of the Invention
This invention relates to optical waveguide lasers and in particular to soliton lasers.
2. Related Art
Ultra-fast light pulse sources will be key components in future high bit rate telecommunications systems and soliton pulse sources in particular are recognised as being valuable for long distance high bit rate systems. A current requirement is for the generation of solitons with picosecond optical pulses and sufficient peak powers for soliton propagation in the 1.55 .mu.m silica optical fibre transmission window.
Although soliton pulses are robust to quite large effects of both chirp and phase noise, the evolution of such pulses inevitably involves the shedding of radiation, leaving behind a less energetic soliton superposed on a continually spreading background component. This dispersive radiation can give rise to interaction between soliton bits and thereby limit the information capacity of the system. The ideal soliton source, therefore, is one providing picosecond duration pulses with temporal, spectral and power characteristics compatible with those of fundamental soliton pulses in the transmission fibre.
One method of generating picosecond pulses is discussed in an article entitled "Mode-locked erbium-doped fibre laser with soliton pulse shaping" by J. D. Kafka, T. Baer and D. W. Hall, Optics Letters 14, No. 22 (November 1989) pp 1269-1271. A mode-locked erbium doped fibre laser is in the form of a ring laser incorporating a 70 m long erbium-doped fibre as the gain fibre, an integrated modulator and a 2 km length of telecommunications fibre. The telecommunications fibre provides a degree of soliton pulse shaping to the pulse produced by the laser.